Different designs of clamping devices which are to be actuated by hand or by fluid pressure, especially by air pressure, are known. These types of clamping devices, for example toggle lever clamping devices, are arranged not only in a horizontal manner, but also under arbitrary spatial conditions. In particular, in the case of overhead design, in the event of a drop in pressure, or when heavy loads are connected to the clamping arm, the clamping arm can move unintentionally into an unwanted position. This can result in damage, in the worst case even in injury.
A toggle lever clamping device is known for example from EP 2 548 700 A1.
Another clamping device which includes features of the present invention is known from DE 298 17 335 U1. It has a housing and a pivotably drivable shaft which is mounted in the housing. As a result of supplying fluid pressure, for example as a result of supplying compressed air to a cylinder of the clamping device or, however, by supplying correspondingly manually applied force by means of a hand lever, said shaft can be moved back and forth between an open position and a closed position of a clamping arm of the clamping device. The shaft is mounted in the housing and is removed out of the housing on the remote sides of said housing. The ends of the shaft are realized as positive locking parts which comprise a square-shaped cross section. The clamping arm which is arranged outside the housing comprises two legs which receive clamping jaws in the region of the ends thereof. As a result, a clamping connection, which is positive-locking with reference to rotation, between the arrangement of clamping arm and clamping jaws and the shaft is generated in the region of the shaft ends between the legs and the clamping jaws. The clamping device comprises a first locking means which is mounted in one of the clamping jaws and is pivotable together with the shaft, in addition a second locking means which is arranged in the pivot path of the first locking means and is mounted in the housing. The two locking means interact releasably in a defined pivot position of the clamping arm. The first locking means comprises a locking segment which is connected fixedly to the clamping jaw and a latching bolt which is connected to said locking segment. With reference to the locking segment, the latching bolt can be arranged in several angular positions with reference to the pivot axis of the clamping arm, for example at an opening angle of 45°, beginning every 15°, up to 135°. The locking segment is provided with blind bores corresponding to said selectable positions of the latching bolt. The second locking means comprises a U-shaped spring which is mounted in the housing, and more particularly, is mounted in a separate component that is connected to the housing. When the clamping arm is transferred into the defined pivot position, the latching bolt contacts the U-shaped spring in the region of the free ends of the two spring legs and expands the spring slightly in order to be moved completely into the recess defined by the spring in the defined position of the clamping arm, the two ends of the spring legs being pulled back such that a pivoting back of the clamping arm out of said defined pivot position is only possible as a result of applying increased torque which acts on the shaft of the clamping device. However, this is dimensioned such that the clamping arm is not able to move unintentionally out of said defined pivot position which corresponds to the previously set opening position of the clamping arm.